Because of the superior mechanical properties and chemical characteristics for which it is well known, polyester resin is widely used not only for clothing and industrial and other textiles, but also as a base material for magnetic tapes, flexible disks and other magnetic recording materials, as a base material for photographs, electrical insulation, cable wrapping, capacitors, evaporation coatings, adhesive tape, printer ribbons and magnetic cards, for mold release of FRP and the like, in packaging, and in various agricultural and other industrial applications.
Recently, there has been increasing demand for improvements in the burn resistance of synthetic fibers and various plastic products from the standpoint of fire prevention, but conventional polyester resin is unsatisfactory in terms of burn resistance. Therefore, efforts have been made to impart flame retardancy by adding organic halogen compounds, antimony compounds and other flame retardants during polyester manufacture and the like.
One problem with these flame retardants is that they produce toxic gas in contact with flame, and it has therefore been proposed that a hydrated metal compound such as aluminum hydroxide or magnesium hydroxide be added instead, but a large amount must be added in order to impart sufficient flame retardancy, detracting from the excellent properties inherent in polyester resin.
To resolve these problems, methods have been proposed whereby specific phosphorus compounds are added or copolymerized as flame retardants during polyester manufacture (Japanese Patent Application Publication Nos. H6-16796, 2001-139784, 2001-163962).
However, these phosphorus-containing polyester resins have often been hardly soluble in toluene, xylene and other widely-used organic solvents. As a result, an extremely low degree of polymerization has been necessary in order to obtain a solution or dispersion of a phosphorus-containing polyester resin for processing textiles or PET films or the like using these widely-used organic solvents, making it difficult to maintain the inherent properties of the polyester resin. It has thus been necessary to use organic solvents with high solubility such as dioxane, DMF, HFIP, OCP and the like so that such phosphorus-containing polyester resins can be coated as base material processing treatment resins for processing, for example, textiles and PET films while maintaining a high degree of polymerization and preserving the inherent properties of the polyester resin, but although these solvents have high solubility, they have problems in terms of working environment and environmental protection.
To resolve these problems, the applicants in this case have proposed including a reactive phosphorus-containing compound in the reaction system during polyester synthesis (Japanese Patent Application Publication No. 2004-67910). In this way, a polyester resin can be made flame retardant while maintaining the excellent properties inherent in polyester resin.
As thus described polyester resin has been made more flame retardant, but the inventors have continued to make improvements in polyester resin in order to further enhance the flame retardancy of polyester resin for purposes of fire prevention and the like, and to impart additional characteristics to the polyester resin for purposes of fire prevention and the like. The inventors also focused on the scattering of high-temperature droplets from polyester resin after combustion when the polyester resin burns, and conceived the idea that even when polyester resin burns, the damage can be prevented from spreading if such scattering of droplets can be prevented.